Blow-moulding is the primary method to form hollow plastic objects such as soda bottles, air ducts and CVJ boots for automobiles, etc. Many variants of the blow-moulding process are known in the art and practiced by the industry. For instance, extrusion blow-moulding includes the steps of clamping the ends of a softened tube of polymer (a parison) in a mould, inflating the polymer against the mould walls with a blow pin, and cooling the product. This method is simple in terms of equipment, and is well-suited to parts with relatively simple geometry, like bottles and almost linear ducts.
Parison manipulation and suction blow-moulding are variants designed to produce ducts with complex three-dimensional geometries, that would be impossible or inefficient to make with straight extrusion blow-moulding. Coextrusion blow-moulding and sequential blow-moulding are designed to optimise the properties of final parts by placing different materials at the most appropriate position in the part. In coextrusion blow-moulding, the parison is made with two or more concentric layers of different materials. In sequential blow-moulding, the parison is made of different materials alternating along its length.
These variant processes are often used in combination, for example sequential coextrusion suction blow-moulding is used to make three-dimensional ducts with two different materials forming an inside and outside layer, these layers having varying thicknesses along the part.
Other blow-moulding methods include injection blow-moulding, as used for example to make bellows and CVJ boots for automotive applications, and stretch blow-moulding, as used to produce soda bottles.
Important factors for blow-moulding include:                Polymer viscosity at high & low shear rates                    Melt strength and sagging (important for uniform wall thickness, no holes)            Crystallization rate (slow rate preferred).                        
These factors are especially important in order to obtain long blow-moulded articles in the extrusion blow-moulding process. They are also important for other blow-moulding processes like suction blow-moulding and sequential co-extrusion blow-moulding.
Thermoplastic vulcanisates (TPVs) are blends consisting of a continuous thermoplastic phase with a phase of vulcanised elastomer dispersed therein. TPVs combine many desirable characteristics of cross-linked rubbers with some characteristics of thermoplastic elastomers. TPVs are typically made using a process called Dynamic Vulcanisation or dynamic cross-linking, which involves mixing a thermoplastic component with a vulcanisable elastomer component, under shear at a temperature above the melting point of the thermoplastic component, in the presence of a cross-linking agent that will act to vulcanise the elastomer component. The rubber is thus at the same time cross-linked and dispersed within the thermoplastic matrix.
There are several commercially available TPVs, for example Santoprene® (Advanced Elastomer Systems) and Sarlink® (DSM) which are TPVs based on an ethylene-propylene-diene copolymer (EPDM) and polypropylene (PP), Nextrile® (Thermoplastic Rubber Systems) which is a TPV based on nitrile rubber and PP, and Zeotherm® (Zeon Chemicals) which is a TPV based on acrylate elastomer and polyamide.
The following documents disclose TPVs:
U.S. Pat. No. 6,774,162 (PolyOne Corporation) describes a TPV of four components (A, B, C, D), comprising a thermoplastic synthetic resin (A); a substantially cross-linked polyethylene (B); a rubber (C) having a degree of cross-linking of >90% and a plasticiser (D); as well as of standard blend ingredients (E) comprising at least one cross-linking agent or cross-linking system, whereby a mixture is comprised of the following quantitative proportions (in % by weight) based on the sum of the four components (A, B, C, D); thermoplastic synthetic resin (A) 5 to 20; polyethylene (B) 25 to 5; rubber (C) 30 to 50; plasticiser (D) 50 to 25; wherein the thermoplastic synthetic resin (A) is a propylene-based homopolymer, block polymer or copolymer with high crystallinity.
WO2001021705(A1) describes a TPV consisting of polypropylene, EPDM (polymer of ethylene, propylene and 5-ethylidene-2-norbornene in a ratio of 63/32.5/4.5 wt %), and oil. The TPV is compounded by melting in an extruder 60 parts by weight polypropylene, 100 parts by weight EPDM, and 140 parts by weight of an oil, and vulcanising.
EP0922730 B1 (Advanced Elastomer Systems) describes a TPV consisting of a blend of ethylene acrylate rubber (Vamac GLS) and poly(butylene terephthalate) (Valox HR 326), dynamically vulcanised with a bisoxazoline curative, and a further TPV consisting of ethylene acrylate rubber (Vamac GLS) with a co-polyetherester (Hytrel® 8238).
WO 2004/029155 (E.I. DuPont de Nemours) discloses a curable thermoplastic blend comprising (a) from 15 to 60 wt % of a polyalkylene phthalate polyester polymer or copolymer and; (b) from 40 to 85 wt % of a cross-linkable poly(meth)acrylate or polyethylene/(meth)acrylate vulcanisate rubber in combination with an effective amount of peroxide free-radical initiator and an organic diene co-agent to cross-link the rubber during extrusion or injection moulding of the curable thermoplastic elastomeric blend. When the curable blend is melt extruded, the result is a TPV that can be processed in many ways like a thermoplastic, but which has the characteristics of a cross-linked rubber.
Although known TPVs have interesting properties, a continuing need exists for new TPVs that exhibit desirable characteristics for processes like blow-moulding, while having high performance characteristics, such as resistance to heat, wear, and resistance to oil and solvents. In particular, due to the tendency towards part and function integration for a reduced overall system cost, the automotive industry demands ever increasing performance from plastic materials, both in terms of processing and mechanical properties.